The present invention relates to a microparticle spraying apparatus and to a microparticle spraying method and a method of manufacturing a liquid crystal display device, which utilize said apparatus.
With advances in electronics, microfine microparticles are used in a variety of applications. Among such microparticles are electrically conductive microparticles in use in anisotropic films, conductive microparticles in use in the field of bonding technology, and microparticles applied as spacers in liquid crystal display devices.
As one of the applications of such microparticles, the liquid crystal display devices have been broadly used in personal computers and portable electronic appliances. The liquid crystal display device generally comprises a pair of substrates 1, a liquid crystal layer 7 sandwiched therebetween, a color filter layer 4, a black matrix layer 5, a transparent electrode layer 3, alignment layers 9, etc. as illustrated in FIG. 12. Here, it is a spacer layer 8 that defines the interval of two substrates 1, i.e. the proper thickness of the liquid crystal layer.
In the conventional method of manufacturing a liquid crystal display device which comprises spraying spacer microparticles randomly and uniformly over a substrate carrying pixel electrodes, the spacer microparticles are inevitably disposed as well on the pixel electrodes, i.e. the display areas of the liquid crystal display, as can be seen from FIG. 12, with the result that the aperture rate is substantially decreased. The spacer microparticles are generally composed of synthetic resin, glass or the like and when the spacer is disposed on pixel electrodes, light leaks occur in the spacer region owing to a depolarization effect. In addition, the orientation of liquid crystals on the spacer surface is disturbed to cause escape of light, resulting in decreases in contrast and tone to aggravate the display quality.
In order to overcome the above disadvantages, the spacer microparticles should be disposed exclusively in the light-shielding black matrix areas formed in the color filter layer. The black matrix layer is provided for improved contrast of display in the liquid crystal display device and, in the case of a TFT liquid crystal device, for preventing the optically erratic action of the cell due to external light.
As the technology directed to disposing a spacer selectively in the black matrix areas, i.e. in the areas other than pixel electrodes of a liquid crystal display device, Japanese Kokai Publication Hei-4-256925 discloses a method which comprises holding the gate electrode group and drain electrode group at the same electric potential during application of the spacer microparticles. Japanese Kokai Publication Hei-5-53121 discloses a method which comprises applying a voltage to the wiring electrodes during application of the spacer microparticles. Moreover, Japanese Kokai Publication Hei-5-61052 discloses a dry microparticle spraying method which comprises applying a positive voltage to the wiring electrodes and a negative charge to the spacer microparticles.
However, any method as mentioned above invariably depends on the use of wiring electrodes and, therefore, are only applicable to TFT liquid crystal display devices. In STN liquid crystal display devices, there are no electrodes corresponding to said wiring electrodes but stripe electrodes are disposed in orthogonal relation between the two substrates to form pixel electrodes, with the areas corresponding to the black matrix forming the electrode gaps (spaces), with the result that the above technologies cannot be utilized.
Meanwhile, Japanese Kokai Publication Hei-4-204417 discloses a technology wherein the spacer is selectively disposed in the electrode-free areas by charging the electrodes on one of the insulating substrates and spraying the spacer charged to the same polarity as the electrodes over the insulating substrate and, in addition, a conductor is disposed under the electrode substrate in a microparticle spraying apparatus so that a plus voltage may be applied so as to control the falling speed of the negatively charged spacer while the housing comprises a conductive material to which a minus voltage may be applied for avoiding attraction of the negatively charged spacer microparticles to the apparatus wall.
However, there is some variation in the charging amount of the spacer due to the intrinsic variation of the spacer material itself, with a portion of the spacer being charged to the opposite polarity, and such reversely (positively) charged spacer microparticles are disposed on the electrodes (which are negatively charged) on the insulating substrate to substantially reduce the aperture rate.
Japanese Kokai Publication Sho-63-77025 discloses a spacer spraying apparatus wherein the ceiling and bottom of the apparatus are constituted as a pair of electrodes so that an electric field may be generated by applying a direct-current voltage across said ceiling and bottom and the spacer equalized to the ceiling in electric potential is sprayed. Because, with this apparatus, the spacer is caused to fall through the electric field, the falling speed of the spacer can be controlled so that the spacer microparticles can be uniformly dispersed and deposited on a substrate.
However, with this spacer spraying apparatus, the falling speed of spacer microparticles can be controlled in some measure by exploiting the influence of an electric field but since lines of electric force are formed between the top and bottom electrodes, selective control of spacer falling position is difficult. Moreover, when a voltage is applied to the stripe electrode array for use as bottom electrodes, no selectivity is obtained but a uniform electric field prevails because of the narrow electrode gaps in the liquid display device. Thus, it is even more difficult to dispose the spacer selectively in the electrode gaps where no pixels exist.
Japanese Kokai Publication Hei-1-187533 discloses a spacer spraying apparatus wherein a spraying chamber is connected to a spacer supply tank through a pipeline and, using a gas as the vehicle, the spacer is fed from the spacer supply tank to the spraying chamber.
However, this spacer spraying apparatus is not designed for selective control of spacer falling position and incapable of preventing disposition of spacer microparticles on the display areas of the liquid crystal display device.
The present invention has for its object to overcome the above-mentioned disadvantages and provide a microparticle spraying apparatus with which the disposition of microparticles on a substrate carrying electrodes can be accurately controlled, particularly a microparticle spraying apparatus capable of selectively disposing spacer microparticles in electrode gaps where no pixels are present even on a substrate carrying an array of stripe electrodes in use for the STN liquid crystal display device, to a microparticle spraying method and a method of manufacturing a liquid crystal display device which utilize said apparatus.
The first aspect of the present invention relates to a microparticle spraying apparatus for selective disposition of a charged microparticle on a substrate carrying a plurality of electrodes
which comprises a spraying chamber adapted to accommodate said substrate, a microparticle supply means for supplying said microparticle into said spraying chamber and spraying it on said substrate, and a voltage application means for applying voltages to the electrodes disposed on said substrate,
said voltage application means being capable of applying different levels of voltages to said electrodes respectively.
The second aspect of the present invention relates to a microparticle spraying method
comprising applying an electric potential to a plurality of electrodes on a substrate, charging a microparticle electrostatically, and spraying and disposing said microparticle selectively on said substrate,
wherein a microparticle spraying apparatus includes a means for eliminating an oppositely charged microparticle.
The third aspect of the present invention relates to a microparticle spraying method
comprising applying an electric potential to a plurality of electrodes formed on a substrate, charging a microparticle electrostatically, selectively spraying and disposing said microparticle on the substrate,
wherein a charged element with an electric potential of the same polarity as said charged microparticles being applied is disposed in at least a domain of the surface extending from the nozzle orifice of a microparticle delivery nozzle duct to the periphery of said substrate.
The fourth aspect of the present invention relates to a microparticle spraying method
comprising spraying plural kinds of microparticles constituted by dissimilar constituent material or surface composition from the corresponding microparticle tanks with a pressurized gas as the vehicle using a microparticle spraying apparatus,
wherein said microparticle spraying apparatus comprises a spraying chamber for accommodating a substrate, a microparticle supply means comprising at least one microparticle delivery nozzle duct and at least one microparticle tank, both for supplying a microparticle into said spraying chamber and spraying it onto said substrate, and a voltage application means for applying voltages to a plurality of electrodes formed on said substrate,
said voltage application means being capable of applying dissimilar levels of voltages to each of said electrodes.
The fifth aspect of the present invention relates to a method of manufacturing a liquid crystal display device
which comprises using the above-mentioned microparticle spraying apparatus,
disposing a spacer selectively on a substrate carrying a stripe electrode array constituted by a plurality of linear transparent electrodes arranged in parallel, and
applying a relatively high level of voltage to an even number of linear transparent electrodes arranged in parallel and a relatively low level of voltage to an even number of linear transparent electrodes neighboring said even number of linear transparent electrodes to thereby produce a region with a relatively high potential (+(positive)) and a region with a relatively low potential (xe2x88x92(negative)) in an alternate pattern and, in this condition,
further spraying either a positively (+) charged spacer or a negatively (xe2x88x92) charged spacer onto said substrate or
further spraying a positive (+) charged spacer and a negatively (xe2x88x92) charged spacer alternately or in succession onto the substrate.